Fine feed mechanism for grinding machines and the like



Aug. 25, 1959 R. VULLER FINE FEED MECHANISM FOR GRINDING MACHINES AND THE LIKE Filed Nov. 20, 1958 FINE FEED MECHANISM FOR GRHVDING MACHJNES AND THE LIKE Rolf Viiller, Haus Ruckle, Dagersheim, Boblingen, Germany, assignor to Fortuna-Werke Spezialmaschinenfabrik AG., Stuttgart, Germany Application November 20, 1958, Serial No. 775,145

Claims priority, application Germany November 20, 1957 12 Claims. (Cl. 51-165) The invention relates to an arrangement for producing fine feeding movements, and more particularly such movements between a material removing device, such as a grinding wheel, and a Work piece.

With presently known arrangements it is hardly possible to obtain the required accuracy of the removal of material from a work piece, because of the very small tolerances now required in many machine parts. It is often necessary that the removal of material be exact down to tenths or even thousandths of a millimeter.

The feed of the grinding wheel per rotation of the workpiece is then often merely a fraction of a micron (,u). A further requirement for perfect grinding, however, is exceptional rigidity of the structure against machine vibrations, which can adversely eifect the shape of the finished article. The grinding wheel and the work piece must therefore be held on the machine frame as rigidly as possible. The requirements of rigid mounting and very fine feed cannot be met by present machines.

Mechanical feeding devices using gear drives or rack or endless screw arrangements, which rely on the operation of a slow moving screw spindle are inaccurate and uneven. Hydraulic arrangements in which the pressure medium is throttled, even when stepped piston ratio reduction devices are used, are dependent to a great degree upon the viscosity of the pressure medium which varies with the temperature.

It has also been proposed to produce a fine feed with out movement of the support merely by increasing the rate of rotation of the grinding spindle, so that as a consequence of the unbalance the increased speed of rotation produces increased amplitude of vibration of the grinding wheel shaft. But such a procedure is dangerous because the permissible rotation speed of the grinding wheel is exceeded and because it produces by reason of these vibrations unbalance in the machine. Also, it does not produce a clean ground surface. Besides, grinding wheels used in modern grinding machines are usually so accurately balanced that this type of device will not work.

Small feed movements are also produced as the difference between two oppositely directed movements, in which the main forward feed of a first slide is only slightly greater than the backward movement of a cooperating second slide. But the driving arrangement required for this double movement favors the production of vibrations in the machine which reduce the accuracy and neatness of the grinding.

It is recognized that, after the stopping of the forward feed of the grinding supports and before the rapid backfeed, in consequence of the gradual equalization of the grinding pressure, a small relative movement between the grinding wheel and the workpiece always occurs, which can be detected as a small forward movement during the grinding.

-It has therefore been suggested to measure the pressure between the wheel and the work and to regulate the grinding time accordingly; stopping the machine automatically or manually when a predetermined end pres- States Patent I any desired characteristic by controlling heat furnished per unit of time.

wheel, so that accurate results can not be assured. This then does not constitute a solution to the problem.

Fine feeding with a piston rod feed is also known, but this is not suited for grinding machines because the degree of feed increases instead of decreasing. A fine feed with decreasing degree of feed can be attained by swinging the grinding wheel support about an axis which is parallel to the grinding wheel shaft. A variation of the piston rod feed, but with the desired decreasing degree of feed, involves a construction in which a flat sheet, pressed out by a transverse force, through a bell-crank lever can, in the fine feed range, produce very small movements with very large feeding force, giving an even feed. To push out the longitudinally resilient plate to produce the desired feed movements, corresponding transverse pressure is required. If the plate is made of large cross-section in order to give it greater rigidity with regard to the machine vibrations, the transverse force is very large. This large force must be taken up by the machine parts, such as the frame, and requires mechanism for producing it. If, on the other hand, only small transverse forces are to be used, the cross-section of the plate, must be so slight that it has no stability against vibra-' mitting parts, these are not rigid enough to prevent the development of vibrations.

With the use of slide guides it is possible with known devices to attain a grinding accuracy of 5 to 10 ,1/., measured at the diameter. When roller guides are used, the accuracy may be 1 to 3 ,u. However, because of the small friction losses, these machines are much more sensitive to machine vibrations than those with slide guides. The transmission systems for fine feed of known machines are not rigid enough to damp these vibrations. As a consequence of these vibrations, the surface of the workpiece is defaced by a pattern which corresponds to the vibrations. Attempts heretofore made to damp these vibrations and to make the roller guide less sensitive have, as

the damping increased, reduced the accuracy of the ma;

vice which utilizes roller guides, and gives accuracy while at the same time damping vibrations.

According to the invention, between the tool carrierand the lower slide, on which it is guided by roller guides, a vibration-damping connection is provided which is rigid in its longitudinal direction but the length of which can be changed, which transmits all shifting forces exerted on it along its longitudinal axis, the changes in length being produced by temperature changes in the connecting member. Such a thermal device utilizes the increase in amplitude of vibration of the molecule which occurs with increase in temperature and extracts its power and movement for the feeding. The expansion is, in a desired range, linear with respect to temperature in accordance with physical principles. It is possible by the use of auxiliary devices to provide a working operation having the amount of This thermal feed system consists in heating a connectmg member, for example an expanding rod, which is connected between the tool carrier and its lower slide so, that the rod expands and supplies the feed movement. Thls operation takes place at the conclusion of the usual rapid or coarse feed. The tool carrier is then moved with relation to the stationary lower slide in accordance with the slow expansion of the rod. When the desired degree of feed is reached and the workpiece has the desired final shape, the supply of heat is cut off and the rod is cooled, after which the usual quick return motion of the grinding supports can be initiated. By regulatlng the amount of heat supplied per unit of time, any desired amount and rate of feed-can be obtained. For heating and cooling various fluids can be used, but in order to produce the desired feed characteristics most readily it is advantageous to heat by an electric current and to cool by a cooling medium which is used in connection with grinding machines such as water or a cooling emulsion.

The feed device may consist of an expansion rod, which has inside it a ceramic heating body or a ceramic carrier with an electric heating coil. The heating space is completely closed except for the lead wires for the electric current. The rod also has a cooling jacket which is connectedto the cooling medium circuit of the grinding machine. The flow of cooling medium is controlled by a suitable means such as a magnetically operated valve. The rod is connected with the upper and lower slides without any play. If, for connecting the rod with the upper and lower slides. forked brackets with cooling zones connected to the cooling water supply are used, the distance between the slides and the alignment of the bolts and the brackets need agree only approximately.

For the usual fine feed of 2.5 /seo, a heating current of 0.75 kw. is enough. For very fast up to coarse feed of 10 g/sec., 2 to 3 kw. is necessary. The rate of feed is controlled by the supply of current, which may be determined by a wattmeter in the heating circuit calibrated in 11/860. of feed. The amount of feed depends also on the time of heating, which can be controlled by a time relay. If the heating current is controlled in a known way by means of cams and resistances, any desired feed characteristic and/or any functional relationship between the feed and the grinding time can be obtained.

The end of the grinding can be controlled by measurement of the workpiece by a measuring device which cuts off automatically when the proper dimension is reached, or through grinding until the slide meets a stop. But it can also be stopped at the end of a predetermined heating period, with or without cutting off of the heating, by starting the cooling, and in general the machine can be controlled in any desired manner.

For normal fine feed, an increase in temperature of the expansion rod of only 7 to 14 C. is necessary. When the rod is hot, the cooling must remove about to 8 kcal. The feed takes place with a large reserve of force, so that the thermal feed of the slides can be accomplished with undiminished accuracy. With a rod of about 50 mm. diameter for each 11. of feed a feeding force of about 140 kg. results. This lies above the value of the initial stress of the feed mechanisms of medium-sized grinding machines.

It has been found that the stability against vibrations of a roller guided device with thermal feed is twice as great as that of a slide guided device with ordinary feed,

and is more accurate.

Further objects and advantages of the invention will appear more fully from the following description especially when taken in conjunction with the accompanying drawings, which form a part thereof.

The drawing shows in side elevation, with parts in section, a feed device embodying the invention.

' The upper slide 1 of a grinding machine is guided by guide rollers 2 on a lower slide 3. The upper slide may carry a support for a grinding wheel, while the lower support is movable by means of coarse feed mechanism on a frame on which the workpiece holder is rigidly mounted. Fastened on the upper slide is a bracket 4 in which fits a bolt 5, and on the lower slide a bracket 6 with bolt 7. A hollow expansion rod 8 is formed of a material such as a metal having a substantial thermal coefficient of expansion. Secured on each end of the rod 8, as by threads 11, are forked caps 9, 10, the legs of which fit over the brackets 4, 6 and engage bolts 5, 7 respectively. The bolts are tightly fitted in the brackets and caps so that the whole assembly is free of play, and the upper and lower slides are thus connected together without play.

The hollow space 12 inside rod 8 is tightly closed at each end by plugs 15. A ceramic heating body 13 is positioned inside space 12 by means of insulating rings 14 and is fed with current by lead-in wires 16, 17 which pass through the caps 9, 10 and plugs 15 and are connected to the heating body by caps 18.

The expansion rod 8 is provided with a cooling jacket 19. The cooling medium enters space 29 within the jacket by pipe 20 and leaves it by pipe 22. The supply of cooling medium is controlled by a magnetically controlled valve 24 in pipe 22. By suitable automatic control means, this valve can be opened at the proper time, and the electric heating means can be regulated, to vary the beginning and end of the grinding as well aS. the quantities of heat and of cooling medium supplied to the rod.

In the bases 21, 23 of brackets 4, 6 are cooling chamber 26, 28 which are fed with cooling medium through pipes 25, 27 respectively, which, like pipes 20, 22, are connected to the cooling fluid circuit of the grinding machine. The cooling of the bracket bases prevents 11B- desired transmission of heat to the slides.

While I have described herein one embodiment of my invention, I wish it to be understood that I do not intend to limit' myself thereby except within the scope of the claims hereto or hereinafter appended.

I claim:

1. In a machine having two relatively slidable carriers, a material removing mechanism and a work holder mechanism, one of said mechanisms being rigidly mounted on one of the carriers, a connecting rod of a material having a substantial thermal coefficient of expansion connected without play to both said carriers, and means for heating and cooling said rod to expand and contract the same to cause relative movement of the work towards and from the material removing mechanism.

2. In a device as claimed in claim 1, the longitudinal axis of said rod being parallel to the direction of the relative movement of the carriers.

3. In a machine having two relatively slidable carriers, a material removing mechanism and a work holder mechanism, one of said mechanisms being rigidly mounted on one of the carriers, a bracket on each carrier rigid therewith, a connecting rod of a material having a substantial thermal coefficient of expansion connected without play to both said brackets, means for heating and cooling said rod to expand and contract the same to cause relative movement of the work towards and from the material removing mechanism, and means for cooling said brackets.

4. In a device as claimed in claim 3, the longitudinal axis of said rod being parallel to the direction of the relative movement of the carriers.

5. In a device as claimed in claim 4, said rod being hollow and said heating means being located inside the rod.

6. In a device as claimed in claim 5, said cooling means comprising a cooling jacket on the outside of said rod and means to supply cooling fluid to said jacket.

7. In a device as claimed in claim 1, said rod being hollow and said heating means being located inside the rod.

8. In a device as claimed in claim 7, said cooling means comprising a cooling jacket on the outside of said rod and means to supply cooling fluid to said jacket.

9. In a device as claimed in claim 1, said cooling means comprising a cooling jacket on the outside of said rod and means to supply cooling fluid to said jacket.

10. In a machine having two carriers having plane parallel opposing surfaces and roller guide means between said surfaces whereby said carriers are mounted for relative movement with respect to one another in a direction parallel to said surfaces, a material removing mechanism and a work holder mechanism, one of said mechanisms being rigidly mounted on one of the carriers, a connecting rod of a material having a substantial thermal coefiicient of expansion connected without play to both said carriers, and means for heating and cooling said rod to expand and contract the same to cause relative movement of the work towards and from the material removing mechanism.

11. In a device as claimed in claim 10, the longitudinal axis of said rod being parallel to said surfaces.

12. In a machine having two carriers having plane parallel opposing surfaces and roller guide means between said surfaces whereby said carriers are mounted for relative movement with respect to one another in a direction parallel to said surfaces, a material removing mechanism and a work holder mechanism, one of said mechanisms being rigidly mounted on one of the carriers, a bracket rigid with each carrier extending towards the other carrier and terminating substantially in a plane intersecting the space between said plane surfaces, a connecting rod of a material having a substantial thermal coefiicient of expansion connected 'without play to both said brackets, means for heating and cooling said rod to expand and contract the same to cause relative movement of the Work towards and from the material removing mechanism, and means for cooling said brackets.

References Cited in the file of this patent UNITED STATES PATENTS 2,150,749 Price et a1. Mar. 14, 1939 2,843,974 Butterworth July 22, 1958 2,843,975 K'amm July 22, 1958 2,843,976 Silver July 22, 1958 

